Fixed Supply

A fixed-supply coin has a predetermined total supply that cannot increase after creation. No additional tokens can ever be minted because the minting capability (TreasuryCap) is locked or destroyed during initialization. Fixed supply is common for governance tokens, utility tokens, and any asset where scarcity is a design requirement.

This pattern involves 3 steps during the module's init function:

1. Create the currency: Call coin::create_currency with a One-Time Witness to create the TreasuryCap and CoinMetadata. The create_currency function takes parameters for the coin's decimals, symbol, name, description, and icon URL.
2. Mint the total supply: Call coin::mint with the TreasuryCap to create all tokens at once. The amount is specified in the smallest unit (base units). For example, if your coin has 9 decimals, a supply of 10_000_000_000_000_000_000 represents 10 billion coins.
3. Lock the TreasuryCap: Store the TreasuryCap as a dynamic object field on a permanent object. This prevents anyone from calling coin::mint again because the TreasuryCap is no longer directly accessible. You can also freeze or destroy the TreasuryCap depending on your requirements.

File not found in manifest: I2/fixed_supply/sources/silver.move. You probably need to run `pnpm prebuild` and restart the site.

Why lock the TreasuryCap

The TreasuryCap is the capability that authorizes minting and burning. If you transfer it to the deployer's address instead of locking it, anyone who gains access to that address (through key compromise or social engineering) can mint unlimited tokens. Locking the TreasuryCap as a dynamic object field makes it inaccessible to any function call, including coin::mint (Security Best Practices).

Why burn the UpgradeCap

To further ensure the package cannot be modified, burn the UpgradeCap rather than transferring it. If the UpgradeCap remains accessible, a future upgrade could add a function that extracts the locked TreasuryCap from its dynamic field and mints additional tokens. Burning the UpgradeCap makes the package immutable and the fixed supply permanent (Security Best Practices).

caution

Burning the UpgradeCap is irreversible. You cannot fix bugs or add features to the package after burning it. Only burn the UpgradeCap when you are confident the package is production-ready.

Deploy and verify

To deploy a fixed-supply coin:

1. Build the package:

   $ sui move build

2. Publish to the network:

   $ sui client publish

3. Verify the total supply by querying the CoinMetadata object returned in the publish transaction. The supply field should match your intended total.

View the full example on GitHub.